In order to identify high biological quality watersheds for inclusion in the Healthy Waters Initiative, DEQ has conducted a thorough review of biological monitoring data to identify least disturbed sites sampled throughout the Commonwealth. DEQ includes associated watersheds and riparian buffer land use information for consideration on where conservation efforts may be most beneficial.
All analyses and visualizations were produced in R, an open source statistical language.
Biological monitoring of streams and rivers is an integral component of DEQ’s water quality monitoring program. Biomonitoring allows DEQ to assess the overall ecological condition of streams and rivers by evaluating stream condition with respect to suitability for support of aquatic communities. In Virginia, benthic macroinvertebrate communities are used as indicators of ecological condition and to address the question of whether a waterbody supports the aquatic life designated use.
DEQ uses multimetric macroinvertebrate indices, specifically the Virginia Stream Condition Index (VSCI) and the Virginia Coastal Plain Macroinvertebrate Index (VCPMI), to assess the aquatic life use status of wadeable streams and rivers. The VSCI and the VCPMI are applied to biomonitoring data collected in freshwater non-coastal areas and freshwater coastal areas, respectively. These indices include several biological metrics that are regionally calibrated to the appropriate reference condition (DEQa 2006; DEQ 2013). Results are calculated into a single value, or score, that is sensitive to a wide range of environmental stressors.
To identify recently sampled, high quality sites, DEQ filtered all stations sampled since 2013, averaged SCI scores, and removed sites that fell below VSCI scores of 72 or VCPMI score of 56. Best professional judgement removed additional sites that met biological thresholds but did not uphold the qualification of “best available.”
Upstream watersheds of all stations meeting biological filters were delineated using USGS StreamStats watershed delineation tool. Stream segments ( 1:100k National Hydrography Dataset ) contained within each of these watersheds were buffered by 120 meters to identify a consistent riparian buffer area. Land use within the riparian buffer was analyzed using the most recent National Land Cover Database ( 2016 NLCD). Total watershed area, riparian buffer area, and riparian land use metrics are provided to DCR for further review.
DEQ identified 173 unique, high quality watersheds for DCR consideration. These sites span the Commonwealth are are not limited to one physiographic region. Stations and watersheds put forth for review by DCR are presented in the interactive map below.